1. Field of the Invention
This invention relates to a filter assembly for collecting material that is entrained in a gas stream such as particulate solid material or liquid in an aerosol form, and to a tubular filter element for location in a housing to collect such material.
2. Present Stated of the Art
Filtration of gas in a compressed gas system is generally required so that the gas is sufficiently clean for a subsequent application or to minimise adverse effects of impurities on components of the system. For example removal of compressor oil can be required to minimise chemical contamination and accumulation on valves which might lead to malfunction of the valves, and removal of particulate solid material can be required to minimise abrasion.
A known filter assembly for use in compressed gas systems is sold by Domnick Hunter Limited under the trade mark OIL-X. It comprises a housing having inlet and outlet ports for the gas stream that is to be filtered, and a tubular filter element which can be located in the housing and is configured for the gas stream to flow through its wall, for example generally outwardly from the inside of the filter element to the outside. When the assembly is used to collect liquid in the gas stream (for example which is carried in the stream as an aerosol), the filter element will cause the liquid to coalesce. Coalesced liquid then drains from the filter element and collects in the housing for discharge. For such applications, the housing will include an outlet for discharge of any collected liquid.
The housing of such a filter assembly comprises a body section in which the tubular filter element is located and in which a reservoir for any collected liquid can be provided, and a head end cap with the inlet and outlet ports for the gas stream. The filter element comprises a filter medium and first and second end fittings by which the filter medium is supported within the housing. The end fitting at the end of the filter element remote from the head end cap is connected to the housing end cap by means of a tie rod which extends through the tubular cavity within the filter element and engages the end cap by means of a thread. The seal between the filter element and the end cap can depend to a degree on the accuracy with which the assembler interconnects the element and the end cap using the tie rod. A less reliable seal might result if for example the threads on the tie rod and the end cap are dirty which restricts mating of the threads. Moreover, the assembler may not be able easily to detect this defect.
The present invention provides a filter assembly in which a tubular member is sealingly connected to a housing in fluid communication a port therein, and bears a resiliently deformable tang which can be received in a recess in the housing when the tubular member and the housing are properly assembled.
Accordingly, in one aspect, the invention provides a filter assembly for collecting material that is entrained in a gas stream, which comprises:
(a) a housing having inlet and outlet ports for the gas that is to be filtered, in which a tubular filter can be located arranged for the gas stream to flow through its wall provided by a filter medium, and
(b) a tubular member which can be sealingly connected in fluid communication with one of the ports in the housing, the tubular member bearing at least tang,
the housing having a recess in its internal side wall in which the tang can be received when the tubular member is properly located within the housing to form a seal to the said port.
The assembly of the invention has the advantage that the assembler can recognise when a secure connection has been made between the tubular member and the housing once the tang has been received in the recess. Furthermore, by appropriate configuration of the tang and the recess, the location of the tang in the recess can prevent inadvertent or unwanted separation of the housing and the filter element. Accordingly, the invention provides control over the seal that is formed between the housing and the tubular member. This is important to ensure safe and efficient operation of the assembly.
Generally, the housing will comprise an end cap and a body section in which the filter element is located when the assembly is in use. One or more ports for gas to be filtered can then be provided in the end cap; the end cap can then accommodate the flow conduit within it when the assembly is in use to provide a flow path for gas to be filtered between one of the ports and the filter element located in the housing body section. A filter assembly which comprises a housing having a body section and an end cap, with a flow conduit received in the end cap, is disclosed in WO-A-99/30799 (which claims priority from UK patent applications nos. 9726415.4 and 9815959.3 and which has the same filing, priority and publication dates as the present application). Subject matter disclosed in that document is incorporated in the specification of the present application by this reference.
When the housing comprises an end cap and a body section, the assembly of the invention has the advantage of facilitating assembly of the housing. The tang can retain a filter element engaged with the end cap prior to assembly of the end cap and body section of the housing. The operator is therefore able first to assemble together the filter element and the end cap, then to assembly together the body section and the filter element end cap combination.
Preferably, the tang is deformable, especially resiliently, to enable it to be received and located in its recess, especially as the tubular member and the housing are introduced to one another and assembled. Preferably, the tang is arranged so that it is deformed transversely relative to the axis of the filter element. It will generally be deformed transversely inwardly, towards the said axis.
Preferably, the tang includes a projection by which the tang can be depressed to disengage it from the recess. For example, the tang can have first and second projecting portions at or towards its end, arranged at an angle to one another. The first of the projecting portions can be received in the recess and the second projecting portion can be used to depress the tang to disengage the first projecting portion from the recess.
The tubular member can be provided with more than one tang, for example two, three four or more tangs. The arrangement of the tangs around the tubular member will be arranged to match that of the recesses in the housing. Often, when there are a plurality of tangs, they will be arranged with uniform spacing around the tubular member. Different arrangements of tangs and recesses can be used to differentiate products, for example because of different technical specifications, to ensure that a tubular member is always used in an appropriate housing.
The tubular member is in fluid communication with one or more inlet ports or one or more outlet ports in the housing, providing a path for flow of the stream of the gas that is to be filtered between the port(s) and tubular cavity within the filter element that is defined by the filter medium.
Preferably, the recess is provided in the housing so that location of the tang in the recess can provide an indication that the tubular member has been located in the housing.
Preferably, the recess has an associated ramp portion to cause the tang to be deformed as the tang approaches the recess during introduction of the tubular member into the housing. Generally, the ramp is arranged facing along the axis of the filter element so that the tang is deformed when the tubular member is moved along the axis of the assembly. Other configurations of ramp will be appropriate if the movement of the tubular member into the housing involves other movement such as rotation.
Generally, the flow of the gas stream towards and away from the assembly will be generally horizontal. The tubular filter element will generally be arranged vertically so that the port referred to above is arranged at the top of the housing, with the filter element depending below it. The inlet and outlet ports for the gas to be filtered can be provided in an end cap located at the top of the housing; the end cap can be referred to as the head end cap. The element is preferably supported at or towards the end that is remote from the housing port (and the head end cap when the housing comprises an end cap and a body section), especially by means of a support which extend between the filter medium and the side wall of the housing. When the support extends between the side wall of the housing and an end fitting on the filter element, that end fitting will be the bottom end fitting.
The filter element will generally comprise a filter medium and first and second end fittings. Preferably, the support for the filter element is provided on one of the end fittings. In particular, it can be preferred for the support and the end fitting to be provided as a single component, possibly as a result of being formed together for example as a one-piece moulding, or as a result of being connected to one another for example mechanically, or by bonding (with or without an adhesive material).
Preferably, the support extends from its end fitting towards the side wall of the housing generally transversely relative to the longitudinal axis of the filter element. For example the angle between the support and the said axis can be at least about 45xc2x0, preferably at least about 60xc2x0, more preferably at least about 75xc2x0, and possibly 90xc2x0 or more for some applications when the support will be approximately perpendicular to the axis. When the angle between the support and the axis is less than 90xc2x0, it will generally be preferred for the support to be inclined in a direction away from the port in the housing (which will be in the end cap when the housing comprises an end cap and a body section). This has the advantage of enhancing the ability of the support to withstand force exerted by pressurised gas supplied to the housing. Preferably, the housing has an internal support surface on which the support rests when the filter element is properly located within the housing. The support surface can face axially in the housing, towards the end of the housing from which the filter element is inserted into the housing. Accurate positioning of the support surface can ensure that the seal between the filter element and the housing is formed reliably when the filter element is connected to the housing. It can also ensure that a reliable seal is formed between the element and the housing when the body section and the head end cap of the housing are connected to one another.
Preferably, the support comprises at least three limbs which extend between the filter medium and the side wall of the housing. As a result, the filter element is supported stably within the housing, both along and transverse to its axis. The limbs will preferably be narrow when viewed along the axis of the element especially when the filter element is intended to operate in an in-to-out mode in order to minimise accumulation of any coalesced liquid at the base of the filter element. The limbs might include stiffening ribs to enhance their ability to withstand axial loads which might tend to cause them to flex or break. The length and width of the limbs might be such that the limbs appear elongate when viewed along the axis of the filter when they are longer measured transverse to the axis than they are wide measured tangentially to the axis. They might instead have the form of short tabs or tangs when they are shorter measured transverse to the axis than they are wide measured tangentially to the axis. Details of a support on an end fitting of a filter clement are disclosed in WO-A-99/30800 (which claims priority from UK patent applications nos. 9726418.8 and 98154955.1 and which has the same filing priority and publication dates as the present application). Subject matter disclosed in that document is incorporated in tie specification of the present application by this reference.
It can be preferred for the housing to comprise a body section and a base end cap, in which the support surface on which the support rests is provided on the base and cap. Preferably, the support surface on which the support rests is provided at about the interface between the body section and the base end cap. For example, the support surface might be provided on the base end cap at about the interface with the body section, for example in the form of a shoulder or ledge, provided by an end surface or on an internally projecting rib or a recess.
The support surface can be configured to provide positive location of the support, for example to prevent or at least to restrict rotation of the support relative to the housing. Often, the support surface will be continuous around the perimeter of the housing, for example in the form of a ledge.
When the filter assembly is intended for use in applications in which liquid impurities are to be collected, the housing preferably includes an outlet for liquid entrained in the gas stream which coalesces in the filter element. The housing can include a separable base end cap which defines a reservoir into which coalesced liquid can drain from the filter element and which has a valved outlet for discharge of collected liquid from the housing. The reservoir within the housing can provide a xe2x80x9cquiet regionxe2x80x9d in which liquid can collect without excessive turbulence, so that re-entrainment of the liquid is minimised. Preferably, the body section and the base end cap are both open at the interface between them so that the base end cap closes the housing at its lower end. A valved outlet for coalesced liquid can be provided in the base end cap. The reservoir can be made from a material that is transparent. The provision of a reservoir in a separable end cap has the advantage of ready access to the interior of the housing at its lower end, for example for inspection of the element or for inspection, cleaning or replacement of the reservoir or any valve located within it. The body section and the base end cap can both be open at the interface between them so that the base end cap closes the housing at its lower end.
When the housing comprises a separable base end cap, the body section of the housing can be formed with a substantially constant cross-section along its length. This allows the body section to be formed by extrusion. This has the advantages of convenience and of allowing the length of the body section to be selected easily to fit an appropriate filter element. Furthermore, the body section can be formed with formations such as ribs or grooves in its wall extending along its length. Details of a housing which with a body section having a constant cross-section and separable end caps are disclosed in WO-A-99/30803 (which claims priority from UK patent applications nos. 9726419.6 and 9815963.5 and which has the same filing, priority and publication dates as the present application). Subject matter that is disclosed in that document is incorporated in the specification of the present application by those references. Details of a housing whose body has a constant cross-section, with a longitudinally extending internal formation and a communicating transverse formation, are disclosed in WO-A-99/30802 (which claims priority from UK patent applications nos. 9726419.6 and 9815957.7 and which has the same filing priority and publication dates as the present application). Subject matter that is disclosed in that document is incorporated in the specification of the present application by those references.
The filter medium will be selected according to the requirements on the assembly when in use, for example in terms of the nature and quantity of the impurity (for example as to whether it comprises liquid impurity or solid impurity or both) in the gas stream, the degree of filtration required of the medium, the pressure to which the assembly is exposed when in use. When the impurity to be collected includes liquid (which will generally be present as an aerosol for example of compressor oil), the filter medium will preferably be capable of causing liquid droplets to coalesce. Materials suitable for use in a coalescing filter element are known, including those sold by Domnick Hunter Limited under the trade mark OIL-X. Suitable materials include borosilicate and other glass fibres, activated carbon materials, activated silica materials and so on.
Preferably, the housing comprises a head end cap and a body section which can be separated to allow access to the interior of the housing, the support for locating the filter element being provided on the end of the filter element that is remote from the head end cap. When the head end cap and the body section are separated, a filter element within the housing can be inspected and replaced if necessary.
It is preferred that the assembly includes a flow conduit which can be fitted into the end cap, with one end sealed to a port in the end cap, for directing the flow of gas between a port in the head end cap and the filter medium, especially the tubular cavity within the filter element defined by the filter medium. The connection between the flow conduit and the end cap might be temporary when separation of the end cap and the flow conduit is required or it might be substantially permanent. The use of a flow conduit which is fitted into the housing end cap has the advantage that the flow conduit can be made with a configuration that is not restricted by having to be formed as an integral part of the end cap. For example, when the axes of the openings at the opposite ends of the conduit are not aligned, the flow path between the openings can be configured to present a continuous smooth flow path to the gas stream flowing along it between the first and second conduit openings. The smooth flow path can be constructed to reduce restriction of the flow of the gas stream compared for example with a flow conduit which presents a discontinuous flow path which is sharply angled or contains steps or other obstructions. The flow conduit can be made with additional features during its manufacture. For example, a port might be formed in it for connection to means for indicating the pressure within the conduit. A tang might be formed on the flow conduit which can be received in a recess in the housing when the flow conduit is properly located within the housing end cap. This can provide an indication that the flow conduit is properly located, for example by visual inspection or as a result of the tang received in the recess, especially when resiliently deformable so that it can be received in the recess with a snap fit. The flow conduit can be located in its appropriate position within the end cap by means of interengaged ribs on the flow conduit and the end cap respectively. Details of a filter assembly with a separable flow conduit are disclosed in WO-A-99/30798 (which claims priority from UK patent applications nos. 9726415.4 and 9815964.9 and which has the same filing, priority and publication dates as the present application). Subject matter disclosed in that document is incorporated in the specification of the present application by this reference.
The tubular member in the assembly of the invention can be a flow conduit for directing the flow of gas between the filter medium and a port in the housing, especially the tubular cavity within the filter element defined by the filter medium. The flow conduit can have first and second openings which communicate with the port in the housing and the filter element respectively, in which the axes of the first and second conduit openings are not aligned.
When the housing comprises a head end cap and a body section, the filter element is located largely within the body section of the housing. Generally, the connection to the filter element for the flow of gases is made at about the interface between the body section and the housing head end cap. However, the filter element might protrude beyond the end of the body section or the body section might extend bcyond the end of the filter element. The housing body section and the or each end cap should be capable of being connected to one another with sufficient security to withstand internal pressures to which the assembly is subjected when in use. Examples of appropriate connections include threaded and bayonet type connections. Preferably, the assembly includes means for indicating when the end cap and the body section are connected to one another sufficiently securely to withstand the internal pressures. This can have the advantage of also indicating that the low conduit is appropriately located in the housing (whether or not the housing comprises an end cap and a separable body section), for example when the flow conduit engages the body section (directly or indirectly) and it is through the action of the body section on the flow conduit that the flow conduit is forced into the housing end cap. The indication can be visual, for example involving the appearance of a marking in the housing or the flow conduit. The indication can be sensed in other ways, for example by feeling engagement of a resilient member in a recess. The indication means can be provided by the combination of the tang and the recess, whether detected visually or by feel or in some other way. For example, one of the flow conduit and the housing can bear a resiliently deformable tang and the other of the flow conduit and the housing can have a recess formed in it in which the tang is received when the flow conduit is properly located within the housing. In a preferred embodiment, the tang is provided on the flow conduit and the recess is provided in the housing, preferably the housing end cap.
Preferably, the end fittings for the filter element are made from a polymeric material such as a polyolefin, a polyamide, or a polyester. The polymeric material can be reinforced for example by fibres. The use of a polymeric material for the end fittings has the advantage that it can conveniently be formed by a moulding process, with the flow conduit or the support for the filter element according to the design of the filter element for any particular application.
Preferably, the housing is formed from a metallic material such as a steel or an aluminium alloy, in particular to enable the housing to withstand the internal pressures to which it is exposed when in use. Polymeric materials can however be appropriate for many applications, for example when the filter assembly is only to be exposed to moderate pressures in use or has a small size. The metallic or polymeric components can be made by a casting or moulding process although, as mentioned above, extrusion can be preferred if the body section has a constant cross-section.
Preferably, the housing (especially the head end cap thereof) has at least three ports which are to provide between them the inlet and outlet for the gas that is to be filtered. The provision of at least three ports can enable selection of the relative orientation of the inlet and the outlet by selection of the ports in the housing that are to provide the inlet and the outlet respectively. The selection of ports can be achieved by location of a flow conduit within the housing, appropriately aligned with the selected port or ports. The plurality of ports can also allow the assembly to function as a manifold for combining or separating gas streams. The assembly can include an adaptor block having formations in it by which a connection can be made to another component (such as a closure cap for sealing the port against flow of gas, a conduit for the flow of gas to or from the filter assembly, or a connector by which the housing can be connected to a similar port on the housing of another filter assembly), the block and the housing being capable of being sealingly connected to one another with the block located adjacent to one of the ports of the housing to provide for flow of the gas stream between the said other component and the said port.
Generally, the flow conduit between the internal cavity in the filter element and a port in the housing (whether or not it is separable from the housing) will provide a path for the gas stream to flow between the inlet in the housing and the tubular cavity within the filter element for the gas to flow outwardly through the filter medium provided in wall of the element so that the filter element functions in an in-to-out mode. Alternative arrangements are envisaged. For example, the flow conduit can provide a path for the gas stream to flow between the tubular cavity within the filter element and the outlet in the housing after the gas has flowed inwardly through the filter medium, so that the filter element functions in an out-to-in mode.
The assembly of the invention will include the filter element when the assembly is in use. The filter element comprises a tubular body of filter medium and first and second end fittings by which the filter medium is supported within the housing. A flow conduit or the support or both can be provided as part of the end fittings of the filter element, especially when the end fitting (including the flow conduit or the support) is formed by a moulding operation.
The tubular member can be the filter element of the assembly, comprising first and second end fittings having the tubular wall provided by the filter medium located between them, and in which the tang is provided on the first of the end fittings. When the assembly includes a flow conduit, it can be separable from the end cap or the filter element or both. A flow conduit can be provided can be provided on the same end fitting of the filter element as the tang.
In another aspect, the invention provides a tubular filter element for location in a housing to collect material that is entrained in a gas stream by passing the gas stream through the wall of the element, which comprises a filter medium and first and second end fittings by which the filter element can be located within a filter housing when in use, the first end fitting bearing a tang which, when the connection is formed, can be received in a recess in the housing.
Preferably, the tang can be deformed resiliently during formation of a connection between the filter element and a housing, and the recess allows the configuration of the tang to be restored at least partially towards its undeformed configuration.